Process for fast curing alkali metal silicate bonded product



1 0 5 8 cms REFERENCE EXAMINEH Sept. 9, 1969 F. A. DONNER 3,456,354

' PnocEss Fon FAST eurams ALKALI METAL slums oNDED PRODUCT Filed Jan.1s, 1967 AND FORCED 'Al/1 GAS-FIRE!) HEATH/6 72 5547' MEA/VS 260N-2000W? United States Patent O 3,466,354 PROCESS FOR FAST CURINGALKALI METAL SILICATE BONDED PRODUCT Fred Albert Donner, Seattle, Wash.,assignor to Vermiculite Manufacturing Company, Seattle, Wash., acorporation of Washington Filed Jan. 16, 1967, Ser. No. 609,619 Int. Cl.B28b 11/14 U.S. Cl. 264-57 17 Claims ABSTRACT OF THE DISCLOSURE A methodof fast curing a sheet-like mass of mineral berous material containingan aqueous solution of an alkali metal silicate as a binder and having aminimum moisture content of 30% -by simultaneously puncturing one sideof the sheet to form a multitude of perforations while wetting bothsides of the sheet to prevent migration of the binder to the surfacesand then exposing the sheet to a radiant heat source in an oven havingan ambient temperature of 600-2000 F. so as to reduce the moisturecontent to less than 15% in 2-5 minutes time.

BACKGROUND AND SUMMARY OF THE INVENTION This invention relates toimprovements in the manufacture of simulated masonry products formed andcolored to look like brick, stone or the like when installed, or made intile form for oor coverings or for other purposes. While the inventionis herein described in terms of a preferred form thereof, it will berecognized by those skilled in the art that various modifications may bemade therein without departing from the principal features involved.

The invention involves a thin, hard product characterized by relativelycompact or dense nature and high strength, yet light in weight, andcapable of manufacture in different colors and surface textures.

These characteristics are achieved in an improved process which includesthe very rapid removal of water under relatively high temperatureconditions from a thinned sheet of a mixture of dry absorptive fibersand a high proportion, such as 50-70%, of an alkali metal silicatesolution or water glass. The water glass preferably used is of lowalkaline content, e.g. about 10% NazO, 30% Si02 and 60% water.Preferably 2-3% expanded vermiculite is added to impart a slightlygrainy surface texture as explained herein, and a tlecked appearance.Optionally about 1% of a mineral oxide may be added for color.

The ingredients are mechanically mixed and pressformed or rolled into athin sheet which is then sectioned into wafers of the desired productsize and shape while still remaining joined at the edges. The surfacesof the sheet are completely saturated with water, and one or moresurfaces thereof is perforated by means forming spaced holes passingthrough or nearly through to the opposite surface. The sectioned,saturated sheet is then heated rapidly in an oven which preferablyincludes both infrared and forced air heat at a temperature of the orderof 1250 to 2000 F., reducing the water content to a level of from 5% to10% in two to tive minutes time. Lower temperatures might be used, butthe process then takes much longer, and insolubility of the product isgenerally lost if temperatures below 600 F. are used.

Similar products have been made in the past from roughly the sameingredients (but using perlite rather than vermiculite), and by methodsof preparation which involve heat drying a mixture which includes sodiumsilicate or the like. lt has been found that sodium silicate upon dryingmigrates to the surface, weakening the in- 3,466,354 Patented Sept. 9,1969 ICC terior of the product, glassing the surface and preventingescape of the moisture. This property has been compensated for =byrestricting the proportion of sodium silicate and adding perlite tolimit the migration and maintain a more or less uniform distribution ofthe silicate through the material.

Migration of the sodium silicate becomes a particularly serious problemwhen it is sought to speed up the production process, in which case thesurface may quickly become non-porous during the drying step, preventingexit of water from the interior of the material and causing distortionof the product. Different approaches to the manufacture of productscontaining sodium silicate have included permitting the material to drysubstantially at room temperatures prior to hardening it at highertemperatures, or heating the'material very gradually. These techinquesconsume large amounts of time or require the use of variable temperaturefurnaces or a number of furnaces at progressively higher temperatures.Of course consumption of time and requirements for extensive equipmentinvolve higher costs.

Other approaches have included the use of Portland cement or zinc ormagnesium chloride in the presence of their respective oxides or otherchemical additives to combine with the excess water and form a plasticmass, which is then subjected to pressure in a press prior to drying.The additional ingredients are relatively expensive, however, and suchprocesses take longer and result in relatively weak products, oftenrequiring a backing sheet to support them. Centrifugal force has alsobeen used to remove excess water prior to drying.

In accordance with the present invention the result which is sought isto obtain an improved product at less cost and to dry the material veryrapidly to speed production, for obvious economic reasons. The effectsought in the process is to maintain during the drying step a conditionin the material for extremely rapid escape of the moisture in themixture without introducing distortion or other ill effects. In theabove described process the thinness of the material, the perforations,the high proportion of sodium silicate, the vermiculite content, and thesurface saturation are the chief factors operative to achieve thedesired effect.

While an exact chemical description of what takes place during theheating step is not deemed necessary for an understanding of theinvention, an important aspect of the process is that the water on thesheet Surfaces boils continuously during the heating step, maintainingporosity of the surface and permitting rapid escape of substantially allof the water from within the mixture itself within a very few minutes athigh temperatures. Since the sheet is thin, the internal moisture doesnot have far to move. The perforations, preferably spaced about one inchapart, provide additional surface area and paths through which themoisture can escape. Although the high sodium silicate content might beexpected to present a surface glassing problem due to migration,virtually no migration is evident.

The proportions of vermiculite and different mineral oxides may bechosen to vary the texture and color of the final product, whiledifferent surface effects may be achieved by selection of the surfacetexture of the means used to form the sheet into sections. In addition,the vermiculite exfoliates when the sheet is heated to about 1000 F. ormore, imparting a slightly grainy texture to the surface of thematerial, though the percentage of this ingredient is kept low to retainthe required strength.

These and other features, objects and advantages of the invention willbecome more apparent from the foilowing detailed description taken inconnection with the accompanying drawings.

3 BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a somewhat diagrammaticrepresentation of the process according to the invention.

FIGURE 2 is a partial isometric view showing a preferred shape of themanufactured product as it emerges from the process shown in FIGURE l,and showing the perforations on the back side thereof.

DESCRIPTION FIGURE 1 shows a mixing tank 10 for receiving theingredients to be used and mixing them thoroughly prior to formation ofthe resulting mass into a sheet to be sectioned and heat hardened toform facing or tile product units in accordance with the invention. Themixing tank consists of an open-topped vat supported by a base 12 andhaving a curved bottom 14. A motor 16 drives an internal paddle wheel(not visible) on a horizontal axis in a counterclockwise direction. Theingredients are mixed in batches at fifteen minute intervals, in thepresently preferred form of the process.

First, a fiber in dry form is delivered to the tank, and an alkalinesilicate solution and other Optional chemical additives are introducedeither manually or by any suitable conveyor or valve means (not shown).The fiber used is a suitable commercially available one, preferablyasbestos or some other mineral fiber. The fibers should have anabsorbent quality but preferably should not require excessive amounts ofwater or pulping treatment, so that they can quickly 'become completelycoated and :surrounded by the metal silicate during a relatively short'mixing time.

The alkali metal silicate solution is preferably sodium silicate, orso-called water glass, a clear syrup-like substance, and that found towork best consists of about 10% sodium oxide, 30% silicon dioxide and60% water by weight. It is added to the fiber in a ratio of roughly70%-50% sodium silicate solution to 28-35% fiber by weight. Although thebasic product can be made without the addition of expanded vermiculite,this ingredient is preferred to achieve the desired interior and surfacetexture. The maximum preferred percentage is 3% by weight, which`is asignificant amount by volume, but not great enough to weaken the finalproduct. Up to 1% of a mineral oxide chosen for the color to be impartedto the final product is usually added during the mixing stage.

The mechanical mixing is performed without heat or pressure, and whenthe fibers are completely coated by and intermixed with the sodiumsilicate and the other chemical ingredients, the rather plastic andsticky mixl ture is expelled from the tank 10 through a gate 18 by meansof the internal paddle wheel and falls onto a suitable conveyor 20. Thisconveyor moves at such a rate that flow of the material S off the endthereof may be maintained continuous between periodic batch deliveriesfrom the mixing tank 10. Such continuous flow is maintained eithermanually or by a suitable delivery mechanism (not shown) spreading themass of material laterally on the conveyor to be delivered to theforming rollers now to be described.

As it leaves conveyor 20 the material falls between two reductionrollers 22 and 24 which are about six feet long, twenty-four inches indiameter and have a 3/i-inch separation between them. Roller 24 hasflanges 26 which overlap roller 22 to confine the material therebetweenas they turn in directions indicated by arrows, forming the material Sinto a 1% -inch sheet as wide as the rollers themselves.

In combinatiton with each reduction roller is a watering device 28including either a nozzle or a felt pad contacting the roller andconnected to a water supply (not shown) and delivering water insuflicient amounts to saturate both surfaces of the material as itpasses between the rollers. Each roller is preferably coated with Teflonor other suitable thermoplastic nonporous, durable material to inhibitadherence of the material to it.

Suitable takeoff members or guide means 30 deliver the sheet of materialfrom rollers 22 and 24 to the next set of reduction rollers 32 and 34,which are about twenty inches in diameter and have a 3s-inch separationtherebetween. Roller 32 includes flanges 36 on each end overlappingroller 34 to confine the material, and additional watering devices 28cooperate with each roller to maintain the surfaces of the sheet ofmaterial S saturated with water. Guide means 38 deliver the sheet to thenext pair of reduction rollers 42 and 44, which are about sixteen inchesin diameter and have a @i6-inch separation therebetween. Roller 44includes flanges 46 overlapping roller 42, and a watering device 28cooperates with each roller, again to maintain the surfaces of thematerial saturated with water.

Guide means 48 deliver the sheet to the final set of rollers 52 and 54.These rollers have a basic separation of /l of an inch and are notintended to alter the thickness of the material, except to the extentthat they form the sheet into sections of the shape intended for thefinal product. Roller 52 includes flanges 56 overlapping roller 54 toconfine the material as before. Roller 52 carries perforating pins 58spaced approximately an inch apart both laterally and circumferentiallyof the roller. The pins are of length equal to or nearly equal to thespacing between the rollers in order to form perforations which extendfrom the back surface of the sheet to the front although the holes arenot readily visible on the front face. Roller 54 carries knives andridges 60 extending longitudinally and circumferentially to form thesheet S into a waflle pattern of rectangular sections bordered bymargins of reduced thickness and joined by very thin membranes ofmaterial which are easily broken after hardening to separate thesections into singular units of the product being formed. The speeds ofthe four sets of rollers are adjustable to achieve a sheet speed ofroughly 2O to 200 inches per minute.

Watering devices 28' and 28" cooperable with rollers 52 and 54,respectively, preferably comprise a plurality of spray nozzles to whichwater is delivered under pressure. They create a mist and keep both therollers 52 and 54 and the surface of the material saturated. The waterserves also to prevent sticking of the material to the rollers.

Pins 58 on roller 52 pull the patterned and perforated sheet S' fromwallie roller 54, and guide means 62 delivers it to a screen beltconveyor 64 moving in the direction shown. The sectioned sheet S' withall of its surfaces completely saturated with water immediately entersthe drying oven 66.

The size of the oven 66 and the speed of conveyor 64 are preferably suchas to establish a transit time of two to five minutes for any point onthe waflled sheet S to pass through the oven. The oven includes bothinfrared heating means 67, delivering radiant heat to interior portionsof the material, and gas-fired forced-air heating means 69 formaintaining uniformity of heat within the oven chamber and rapidlyremoving the moisture therefrom as it boils to the surface of thematerial. The temperature of the material achieved within the oven issuch as to reduce the moisture content to about five percent in thetwoto five-minute transit time. This hardens the material and thefinished sheet of joined tile units exits on conveyor 64 in the formillustrated in FIGURE 2. As previously indicated, the heavy surfacesaturation maintains the porosity of the surface to permit escape ofwater from the interior of the sheet. The punctured lower surface andthe screened belt conveyor 64 also facilitate moisture removal from thematerial, and because of the thinness of the material the distancethrough which the internal moisture must travel is small.

The resulting product is hard and has a surface texture of ordinarybrick or other textures, depending chiefly upon the roughness of theforming rollers 52 and 54. The surface texture and appearance alsodepends upon the proportions of vermiculite and other optionalchemicals.

As the sheet reaches the end of conveyor 64 the tile sections T arebroken apart along lateral and lengthwise dividing lines 68 and 70formed by the waffle pattern roller 54 and are placed on a cooling beltconveyor 72. The tiles may be packed almost immediately while stillwarm, since their temperature descends to a suitable packing temperaturewithin a few minutes.

The total transit time of the material from the beginning of the mixingstage to the packing step as a final product is less than 30 minutes.The short heat treatment time permits a high production rate. Tile unitsof a size such as illustrated, about 7 inches long and 2 inches wide,can be produced at the rate of approximately 30,000 units per hour andat extremely low cost as compared with masonry and tile productsproduced by previously known techniques.

While the invention has been described herein in terms of a preferredform thereof it will be recognized by persons skilled in the art thatcertain modifications and variations may be made therein withoutdeparting from the principal features involved.

What is claimed is= l. A method of fast curing a thin sheet-like mass ofmineral fibrous material having a thermosetting binder thereinconsisting essentially of an aqueous solution of an alkali metalsilicate, the mass containing at least 30% moisture by weight,comprising simultaneously puncturing one side of the sheet to form amultitude of perforations therein, while wetting both sides of the sheetwith suicient water to prevent substantial migration of the silicatebinder to the surfaces thereof, and thereafter exposing the perforated,surface-wetted sheet to a radiant heat source in a heated oven so as toreduce the moisture content of the sheet to less than 15% by weight intwo-five minutes time.

2. The method according to claim 1 wherein the sheet is perforated bydrawing it between a pair of rollers having water-wetted partingsurfaces and puncturing means thereon.

3. The method according to claim 2 wherein the surfaces of the rollersare wetted by spraying water mist thereon.

4. The method according to claim 2 wherein the surfaces of the rollersare coated with a resinous parting film.

5. The method according to claim 1 wherein the sheet is disposed in theoven so that the non-punctured other side thereof faces the radiant heatsource.

6. The method according to claim 1 wherein the oven is also forced-airheated.

7. The method according to claim 1 wherein the ambient temperature inthe oven is at least 600 F.

8. The method according to claim 1 wherein the silicate is a sodiumsilicate.

9. The method according to claim 1 wherein the solution is a 40% sodiumsilicate solution.

10. The method according to claim 1 wherein the cured sheet issubsequently subdivided.

11. The method according to claim 10 wherein the other side of the sheetis indented for the subdivision process, when the one side thereof ispunctured.

12. The method according to claim 1 wherein the fibrous material iswater absorbent.

13. The method according to claim 1 wherein the mineral fibrous materialis asbestos.

14. The method according to claim 1 wherein the sheet is formed bymixing the fibrous material with 50-70% by weight of 40% sodium silicatesolution.

15. The method according to claim 1 wherein the sheet consistsessentially of fibrous material and the silicate binder therefor.

16. The method according to claim 14 wherein the sheet also comprises upto 3% by weight of expanded vermiculite.

17. The method according to claim 1 wherein the sheet is exposed to aninfrared heat source.

References Cited UNITED STATES PATENTS Re. 17,633 4/1930 ROWe 264-283979,547 12/1910 Norton 25-155 1,693,015 11/1928 Babor et al 106-751,837,146 12/1931 Brooks 264-30 1,881,932 11/1932 POWell 264--631,958,571 5/1934 Gilchrist.

3,055,148 9/1962 Christy 264-309 3,161,554 12/1964 Blackford 264-1563,324,212 6/1967 Paulley et al 264-63 OTHER REFERENCES F. H. Norton,Elements of Ceramics, 1952, p. 114. A. E. Dodd, Dictionary of Ceramics,1964, p. 53.

JULIUS FROME, Primary Examiner I. H. MILLER, Assistant Examiner U.S. Cl.X.R.

